The overall goal is to clone and to study the structure and expression of genes coding for ion channels expressed in heart, especially of the rat. These studies will illuminate the basic molecular mechanisms of the rhythmic electrical activity controlling contraction and relaxation of the heart. The cloned genes will provide a new set of heart specific probes for the study of gene expression in normal and diseased heart tissue. The ion channels of special interest are those coding for voltage sensitive sodium, potassium, and calcium channels. Heart specific chromosomal and cDNA genes coding for sodium channels will be isolated using rat brain dDNA clones already isolated and characterized in these laboratories as probes. cDNAs for voltage sensitive potassium and calcium channels will be cloned by a new method under development in these laboratories. This method is based on high resolution gel electrophoretic fractionation of heart or brain poly(A) mRNA. Fractions that contain an mRNA coding for an ion channel will be identified by microinjection into Xenopus oocytes and electrophysiological assays. Active fractions will be converted into cDNA libraries. Hybrid arrest of translation and an efficient sib selection process will be used to isolate the cDNA clone coding for a given channel.